The present invention relates to a plastic air intake manifold for an internal combustion engine.
Rowbotham, United Kingdom Patent Application No. GB 1,601,817 (=German Patent No. DE 2,822,409) discloses an air intake manifold for an internal combustion engine which is made in one piece from synthetic resin material. This manifold shows that it is possible to design both the attaching flange and the individual duct sections which emanate from a common intake tube in one piece and manufacture it in a single operation. The process of manufacturing such an air intake manifold is quite difficult, however, so that until now it has been necessary to avoid particularly complex shapes.
Schleiermacher et al., European Patent No. EP 251,159 teaches an arrangement in which the leakage gases or blow-by gases which collect in the crankcase of an internal combustion engine are returned to the air intake manifolds of the cylinders. These blow-by gases result from the fact that the piston rings cannot produce a one-hundred-percent seal between cylinder and crankcase. Consequently the blow-by gases, which consist partly of unburned air-fuel mixture and partly of combustion gases, enter the crankcase and must be returned from the crankcase to the air intake manifold. This recycling has the generally known positive additional effect that small amounts of oil vapor accompany it. This oil lubricates the valve seats, so that it is desirable to feed the blow-by gases not just to the intake manifold duct of only one cylinder, but to distribute it as uniformly as possible to all cylinders. To this end, European Patent No. EP 251,159 discloses the use of a separate tube which is inserted into the air intake canister and has openings which are so arranged that each cylinder is supplied with a specific amount of blow-by gases. This additional tube, however, has to be inserted into the air intake canister and is fastened to the canister with suitable fastening means.
Another variant which is described in the above-described state of the art contemplates integrating the return duct directly into the cylinder head. This, however, requires an additional and very complicated machining of the cylinder head. Such integration signifies that the cylinder head must have a bore along its long axis, and this bore is very difficult to make due to its length and its small diameter.
Also known from Ishikawa, Japanese Published Patent Application No. JP 2-37104, is an apparatus for feeding blow-by gas to an air intake manifold, in which two airways communicating with one another are provided in the center between two air intake manifolds situated side by side, one end of each airway being next to the inner circumference of an air intake manifold and the other end leading into an open chamber into which the blow-by gases are introduced. In this arrangement, however, there is a disadvantage that a relatively large number of connections are necessary for recycling the blow-by gases, which thus make the system more liable to trouble.